transListToTreeData() {
    const dealData = (data, isFirst) => {
        const result = [];
        for (const item of data) {
            if (isFirst && item.pid) {
                continue;
            }
            // 自己的id
            const id = item.id;
            // 去data中找有没有自己的孩子（_item.pid === id） >>> filter
            const children = this.departmentList.filter(d => d.pid === id);
            item.departments = dealData(children, false);
            result.push(item);
        }
        return result;
    };
    return dealData(this.departmentList, true);
}